1. Field
The present disclosure generally relates to the design of multi-chip modules (MCMs). More specifically, the present disclosure relates to an MCM that directly couples an optical signal between optical waveguides on different substrates.
2. Related Art
Optical signaling based on silicon photonics has the potential to alleviate off-chip bandwidth bottlenecks as well as provide low latency chip-to-chip communication. Interconnects with these capabilities can facilitate new system architectures that include multiple chips, with multi-threaded cores. For maximal density, the physical package for such a system may employ a combination of planar packaging and vertical chip stacking as needed. An example of such a system is a multi-chip module (MCM) or ‘macrochip’ that includes a logically contiguous piece of photonically interconnected silicon that integrates processors, memory and a system-wide interconnect.
In the macrochip, optical proximity couplers (OPxCs) couple the distributed processors to optical routing layers, which support low-latency, wavelength-division multiplexed (WDM) optical links between chips using silicon-on-insulator (SOI) optical waveguides. These optical waveguides form an interconnect network that provides low-power, high-bandwidth, and high-density communication between the chips in the macrochip. Moreover, each of the chips in the macrochip can be interconnected to every other chip via the WDM optical links that run in orthogonal directions on two routing layers. The optical signals from the chips are coupled into, and between, the routing layers using face-to-face OPxCs.
FIG. 1 presents a block diagram illustrating a side view of an existing MCM with face-to-face OPxCs. In this MCM, an optical signal, which is transported in an optical waveguide on one chip, is reflected out of the plane of the chip surface at a specific angle by a waveguide-integrated mirror on the same chip. This optical signal is then received by an identical waveguide-integrated mirror on another chip, which reflects the optical signal into another optical waveguide on the other chip. However, this approach to optically coupling the optical signal between the chips is often sensitive to alignment and process variations. In addition, the optical path length associated with the optical coupling can result in optical losses because the optical signal is divergent. As a consequence, it can be difficult to obtain high-fidelity signaling in such a multi-chip geometry with low-loss coupling and broadband transmission, which can adversely impact the performance of the macrochip.
Hence, what is needed is an MCM without the problems described above.